Matrix-Assisted Laser Desorption Ionization (MALDI) is a process that generates ions from analyte molecules within a sample. The molecules are initially embedded in a photon absorbing material or matrix as crystals and the matrix is then irradiated by a laser beam to produce desorption and eventually ions. Ionization efficiency is predicated upon the laser beam impacting crystals of analyte and matrix. Groups of crystals are referred to as clusters. If the laser beam is arbitrarily applied to a sample, then the laser beam might not impact crystals at an appropriate position or it might miss the crystals altogether.
There is an ongoing trend in MALDI technology to decrease sample size and increase the number of samples per MALDI plate by decreasing the distance between adjacent samples. The smaller sample size increases the likelihood that a laser beam will miss a sample. In addition, the smaller sample size makes it more difficult to identify an ideal location for laser impact. The increasing number of samples on a MALDI plate is placing a premium on processing speed and efficiency.
Most commercial MALDI systems include a video camera that allows an operator to monitor the actual location where a laser beam impacts a sample. The operator manually checks the location and makes manual adjustments, as necessary. This approach is time consuming. In addition, this manual process is becoming increasingly less useful as the sample sizes decrease.
In view of the foregoing, it would be highly desirable to provide an improved technique for generating ions from molecules within a sample processed by a MALDI system. The technique should be automated for high throughput and should accurately assess samples to identify optimal locations for laser impingement. Preferably, the sample assessment would consider the positions, geometries, and internal distribution of candidate clusters within a sample.